Equipping your drone with a thermal-imaging camera is exactly the same as mounting an ordinary visible-light camera, with one crucial difference: the wavelengths of the photons its sensor detects. Apart from that, everything else works exactly the same, even though you are seeing the world in a whole new way.
To understand the pictures produced by a thermal-imaging camera, let’s first take a moment to understand how we perceive visible light, either with a conventional electrooptical (EO) camera—military-industrial-complex jargon for a video or digital still camera—or even our own eyes. We see the world around us when our retina absorbs photons either emitted or reflected by an object in the environment. Objects that emit visible light include the sun, lightbulbs, and computer screens, and objects that reflect light include every material substance in the universe. An EO camera works in exactly the same manner, substituting an electronic sensor for our retinas.